Does one prostrate during Kaddish and Barechu?
The Shulhan Aruch (O.H. 56:4) lists five instances in which the Shaliah Tzibur should bend forward while reciting Kaddish, and those are 1) Yitgadal, 2) Yehe Sheme Raba, 3)Yitbarach, 4) Berich Hu, and 5) Amen. Neverthteless, Rabbi Yosef Benaim (Noheg Behochma, pg. 191) and Rabbi Elazar Tobo (Pekudat Elazar) write that the custom in Morocco was not to be particular about this, specifically because these prostrations were not enacted by our Sages and are simply a custom.
Regarding congregants bending when “Barechu” is recited, Rabbi Ben Zion Abba Shaul (Or Lezion, vol. II, ch. 5) says similarly, that one should not bow unless enacted by our Sages and in this case it was not enacted. As such, he suggests that one should remain seated when Barechu is recited. Rabbi Shalom Messas (Shemesh Umagen, vol. III, §60 2) also says that the original Moroccan custom was also not to prostrate during Barechu.
That said, it is common for people to stand and bow, and even among those who do not, many at least do slightly rise from their seats during Barechu. The Biur Halacha (§ 113), citing Rabbi Yosef Shaul Nathanson (Magen Giborim), justifies this practice and brings proof from the Tanach (Shoftim 3:20), in which Eglon rose from his throne when Ehud told him the words of Hashem. Therefore, there appears to be a source to bow when one hears Hashem’s Name such as in Barechu. Furthermore, even though some contemporary Poskim write that one should not bow, it appears that the practice to bow is simply a sign of honor when hearing Barechu and is not a full fledged prostration which our Sages were referring to.
Summary: The Moroccan custom is for the Shaliah Tzibur not to particular about the five prostrations during Kaddish. Although the original Moroccan custom was not to rise and bow during Barechu, the common practice is to do so or to at least rise slightly from one’s seat.